1. Field
The disclosed concept pertains generally to electrical switching apparatus and, more particularly, to circuit interrupters, such as, for example, circuit breakers. The disclosed concept also pertains to trip units for circuit breakers. The disclosed concept further pertains to communication methods for such trip units.
2. Background Information
Electrical switching apparatus such as circuit interrupters and, in particular, circuit breakers, are well known in the art. See, for example, U.S. Pat. No. 5,341,191.
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. Molded case circuit breakers typically include a pair of separable contacts per phase. The separable contacts may be operated either manually by way of a handle disposed on the outside of the case or automatically in response to an overcurrent condition. Typically, such circuit breakers include an operating mechanism, which is designed to rapidly open and close the separable contacts, and a trip unit, which senses overcurrent conditions in an automatic mode of operation. Upon sensing an overcurrent condition, the trip unit trips the operating mechanism to a trip state, which moves the separable contacts to their open position.
Industrial circuit breakers often use a circuit breaker frame, which houses a trip unit. See, for example, U.S. Pat. Nos. 5,910,760; and 6,144,271. The trip unit may be modular and may be replaced, in order to alter the electrical properties of the circuit breaker.
It is well known to employ trip units which utilize a microprocessor to detect various types of overcurrent trip conditions and to provide various protection functions, such as, for example, a long delay trip, a short delay trip, an instantaneous trip, and/or a ground fault trip. The long delay trip function protects the load served by the protected electrical system from overloads and/or overcurrents. The short delay trip function can be used to coordinate tripping of downstream circuit breakers in a hierarchy of circuit breakers. The instantaneous trip function protects the electrical conductors to which the circuit breaker is connected from damaging overcurrent conditions, such as short circuits. As implied, the ground fault trip function protects the electrical system from faults to ground.
Modern circuit breaker trip units are generally expected to support multiple different communication (e.g., field bus) protocols without the use of a protocol translator. Traditionally, however, a unique communication adapter has been required for each communication protocol and for each style of trip unit.
It is believed that manufacturers of trip units have taken two approaches to solve this problem. One approach is to integrate one of the many field bus protocols into the trip unit and provide a protocol adapter to convert the native protocol to the desired field bus protocol. Another approach is to provide a plug-in module for the trip unit for each specific field bus protocol. This plug-in module is unique for each trip unit-field bus combination.
There is room for improvement in electrical switching apparatus.
There is also room for improvement in trip units for circuit breakers.
There is further room for improvement in communication methods for such trip units.